The present invention relates to an Al alloy extrusion material for the fuel-distributing pipe of automobile, which improves, in particular, both characteristics of chip separation property and precision of cut face on cutting required for the extrusion material for fuel-distributing pipe used for automobile engine.
In the recent automobile engines, it has become common to use a system directly injecting the fuel into combustion chamber through electronic control for achieving lower pollution or higher output. For this reason, the fuel-distributing pipe is needed for fixing the fuel injection devices to engine and for supplying the fuel into individual fuel injection device, and various fuel-distributing pipes are used. So far, for the fuel-distributing pipe, cast pipe material made of iron or Al alloy has been used. In recent, however, for more improving the quality and the producibility, it has become to be made even with a hollow extrusion material made of aluminum alloy (JIS 6061 alloy; alloy of Al-0.6 wt. % Si-1.0 wt. % Mg-0.25 wt. % Cu-0.2 wt. % Cr). Besides, one example of mounting structure of fuel injection device (hereinafter, referred to as INJ) to the fuel-distributing pipe is shown in FIG. 1. Illustration will be made on FIG. 1. When using a hollow extrusion material (1) as a fuel-distributing pipe, as many holes (3) as the number of INJs are provided on this extrusion material, and INJ (5) is mounted to each of these holes (3) interposing O-ring (4). In the FIGURE, numeral (6) shows an air-intake port and numeral (2) a hole for the pathway of fuel for supplying fuel.
In this case, since the fuel leakage from the joined portion of the wall face of hole (3) of distributing pipe (1) with O-ring (4) of INJ is linked with a serious accident, the sealability of joined portion is considered to be an absolutely necessary condition, thus high precision is required for the precision of face after cutting of the wall face of hole (3) at INJ-mounting portion.
On the other hand, while said JIS 6061 alloy used recently for this fuel-distributing pipe of automobile is excellent in the point of surface precision after cutting, it is very poor in the chip separation property on cutting, arising a problem in the point of producibility.
Moreover, as a 6000-series Al Alloy having corrosion resistance and being free to cut, AA6262 alloy (alloy of Al-0.6 wt. % Si-1.0 wt. % Mg-0.25 wt. % Cu-0.1 wt. % Cr-Pb-Bi) is known hitherto. According to the investigating studies by the inventors, however, this alloy proved to have excellent chip separation property on cutting, but have poor surface precision of cut face on cutting.
For these reasons, the development of Al alloy extrusion material for the fuel-distributing pipe of automobile satisfying both characteristics of high precision cut face and good chip separation property has been earnestly sought for the improved producibility. Besides, in this specification, high precision cut face implies that the face roughness after cutting is very low and there are no defects such as falling on the cut face.
As a result of extensive investigating studies on the Al alloy extrusion material as a fuel-distributing pipe of automobile in view of such situation, the inventors have found that Pb and Bi used most often as improving elements in the cutting property of AA6262 alloy being conventional free cutting Al alloy deteriorate the precision of cut face. In consequence of further investigations, they have developed an Al alloy extrusion material for the fuel-distributing pipe of automobile having allowed both characteristics of high-precision cut face and chip separation property to be compatible by adding only Sn to Al-Mg-Si-Cu alloy and by optimizing the size and distribution density of crystallized grains of Sn compounds.